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Unable to Get a Device Context (using CWnd::GetDC())

Posted on 2002-03-18
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Last Modified: 2013-11-20
I'm writing an application that allows users to place bitmaps on the screen using the mouse. I need to draw bitmaps when the user pushes the mouse button or holds the button and drags. Therefore I can't just use the device context from the OnDraw function, I need to use GetDC() in the OnButtonDown and OnMouseMove functions. This works fine for the first few hundred bitmaps but eventually I get back NULL from the GetDC(). I have checked, and I can't find anyplace that I'm not calling ReleaseDC. Is there any other reason that calling GetDC could fail? It seems like I am using up some resource. Is it possible to get this problem by using up some resource other than device contexts? I have also noticed that once I start getting NULL back from GetDC, none of the other windows in my app will display correctly. By the way, I am using VC++ 5 and running Windows XP.
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Question by:jhanson040697
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5 Comments
 
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Expert Comment

by:shilpa_Jb
ID: 6879277
Hi,
Just check for the return value of the RealseDC() i suspect that its not releasing the resource and hence GetDC
is returning NULL.
-Shilpa
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Expert Comment

by:kirthir
ID: 6879409
Why you want to use GetDC?

U can declare a CClientDC object instead

try this
CClientDC dc(this);
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Expert Comment

by:kirthir
ID: 6879412
The constructor of CClientDC takes care of calling GetDC() and destructor takes of ReleaseDC(),
If you want to do it manually, u need to be more careful in coding
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Accepted Solution

by:
kirthir earned 400 total points
ID: 6879413
The constructor of CClientDC takes care of calling GetDC() and destructor takes of ReleaseDC(),
If you want to do it manually, u need to be more careful in coding
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Author Comment

by:jhanson040697
ID: 6881719
Thanks for the help. I replaced all the GetDCs with ClientDCs an it fixed my problem. I must have missed a ReleaseDC somewhere.
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